This patent application claims priority based on a Japanese patent application, H11-178493 filed on Jun. 24, 1999, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a non-contact type data transmission system that electromagnetically transmits and receives data using a coil or the like but using neither a contact-type connector nor a cable.
2. Description of the Related Art
A typical non-contact type data transmission system comprises a data processing device and a data measuring device. The data measuring device may include an IC card and can be easily moved. Due to the high mobility of the data measuring device, it may be used, for example, to measure the temperature in a room that stores various foods such as vegetables, meat and fish during transport via a transport system. In contrast, the data processing device is relatively large and is usually permanently positioned in an office or a factory where it is used to process the data collected by the data measuring device.
During food transportation by truck, train or plane, for example, the data measuring device is able to operate independently and can measure the temperature. At the completion of transportation, the data measuring device is returned to the office or factory and is inserted into the data processing device. The temperature data collected by the data measuring device is transmitted electromagnetically to the data processing device. The data processing device then processes the received data according to the instructions of the operator of the data transmission system.
In order to electromagnetically transmit and receive the data, the data processing device and the data measuring device each have a coil. The data measuring device is designed to be very small and there is no space for a internal power supply, therefore, its electrical power is supplied by an alternating power supply located in the data processing device. The power supply includes a current supply circuit with numerous transistors, an oscillator that switches the current supply circuit, and a coil used for transferal of the electric power to the data measuring device.
Since the coil in the data measuring device is small, the amount of electromagnetic power generated by the coil is also small. Therefore, it is necessary to ensure that the distance between the coils of the data processing device and the inserted data measuring device is kept as short as possible.
Another potential problem involves a failure of the oscillator within the data processing device which may cause the current supply circuit to continuously apply a direct current to the coil, leading to transistor breakage.
The objective of the present invention is to provide a non-contact type data transmission system that overcomes the issues in the related art as described previously. This objective is achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention.
According to an aspect of the present invention, there is provided a data transmission system including a first device and a second device communicating with each other by electromagnetic induction, wherein the first device comprises a preparing circuit that prepares a data having a voltage defined related to a first threshold; and a transmitting circuit that transmits the data prepared by the preparing circuit, and the second device comprises a receiving circuit that receives the data from the transmitting circuit; a bias circuit that raises the voltage of the received data by a predetermined voltage to produce a sum voltage; and a judging circuit that judges whether the voltage of the data indicates high or low by comparing the sum voltage with a second threshold that is equal to or larger than the first threshold. It is preferable that the receiving circuit includes a coil that produces an electromotive force upon receiving the data from the transmitting circuit, and the bias circuit includes a diode that is connected to the coil in series to increase the electromotive force by a forward voltage of the diode. It is also preferable that the bias circuit further includes a capacitor that stabilizes the given voltage.
According to another aspect of the present invention, there is provided a data receipt device that receives data by electromagnetic induction comprising: a receiving circuit that receives data having a voltage defined related to a first threshold; a bias circuit raises the voltage of the received data by a predetermined voltage to produce a sum voltage; and a judging circuit that judges whether the voltage of the data indicates high or low by comparing the sum voltage with a second threshold that is equal to or larger than the first threshold. It is preferable that the receiving circuit includes a coil that produces an electromotive force upon receiving the data from the transmitting circuit, and the bias circuit includes a diode that is connected to the coil in series to increase the electromotive force by a forward voltage of the diode. It is also preferable that the bias circuit further includes a capacitor that stabilizes the given voltage.
According to still another aspect of the present invention, there is provided a data transmission system including a first device and second device communicating with each other, the first device having a power supply that provides an electric power for the second device using a magnetic field, wherein the power supply comprises an oscillator that generates an oscillation signal; a magnetic field preparing circuit that prepares the magnetic field; a current supplying circuit that supplies a current to the magnetic field preparing circuit according to the oscillation signal; a detecting circuit that detects a halt of generating the oscillation signal by the oscillator; and a switching circuit that turns off the current supplying circuit upon detecting the halt. It is preferable that the oscillation signal includes a plurality of first pulses, the detecting circuit includes a generating circuit that generates a second pulse that permits the switching circuit to keep the current supplying circuit turned on, in response to each first pulse; and a smoothing circuit that smoothes the second pulses; wherein the switching circuit turns off the current supplying circuit in an absence of the smoothed second pulses. It is further preferable that the generating circuit includes a first resistor and a first capacitor that defines a first time constant of the second pulse, and a flip-flop circuit that detects each first pulse to generate the second pulse defined by the first time constant. Similarly, it is further preferable that the smoothing circuit includes a second resistor and a second capacitor that defines a second time constant used for smoothing the second pulses. It is also preferable that the detecting circuit further includes a Schmidt trigger circuit that forbids the smoothed second pulses to force the turning off of the current supplying circuit due to chatter.
According to still another aspect of the present invention, there is provided a device that communicates by electromagnetic induction, comprising a power supply, wherein the power supply includes an oscillator that generates an oscillation signal; a magnetic field preparing circuit that prepares the magnetic field; a current supplying circuit that supplies a current to the magnetic field preparing circuit according to the oscillation signal; a detecting circuit that detects a halt of generating the oscillation signal by the oscillator; and a switching circuit that turns off the current supplying circuit upon detecting the halt. It is preferable that the oscillation signal includes a plurality of first pulses, the detecting circuit includes a generating circuit that generates a second pulse that permits the switching circuit to keep the current supplying circuit turned on, in response to each first pulse; and a smoothing circuit that smoothes the second pulses; wherein the switching circuit turns off the current supplying circuit in an absence of the smoothed second pulses. It is more preferable that the generating circuit includes a first resistor and a first capacitor that defines a first time constant of the second pulse, and a flip-flop circuit that detects each first pulse to generate the second pulse defined by the first time constant. It is preferable that the smoothing circuit includes a second resistor and a second capacitor that defines a second time constant used for smoothing the second pulses. It is also preferable that the detecting circuit further includes a Schmidt trigger circuit that forbids the smoothed second pulses to force the turning off of the current supplying circuit due to chatter.
According to still another aspect of the present invention, there is provided a data receipt method used for a data receipt device receiving data by electromagnetic induction comprising: receiving a data having a voltage defined related to a first threshold; increasing the voltage of the received data by a predetermined voltage to produce a sum voltage; and judging whether the voltage of the data indicates high or low by comparing the sum voltage with a second threshold that is equal to or larger than the first threshold. It is preferable that the increasing includes raising the voltage of the received data by the predetermined voltage defined by the firth threshold and the second threshold.
According to still anther aspect of the present invention, there is provided a power supplying method used for a device that communicates by electromagnetic induction comprising: generating an oscillation signal; supplying a current according to the oscillation signal; preparing a magnetic field using the current; first detecting a halt of the generating of the oscillation signal; and turning off the supplying the current upon detection of the halt. It is preferable the power supplying method further comprises second detecting the generating of the oscillation signal; and allowing the supplying of the current during detection of the oscillation signal.
This summary of the invention does not necessarily describe all necessary features, thus, the invention may also be a sub-combination of these described features.